Artificial lighting of horticultural growths is known in the art and can be used instead of solar light or in addition to solar light.
In the field of plants, research is going on in particularly those processes which are driven by the chemical capture of light energy. At the same time, research into new methods of converting electricity into light of particular wavelengths has led some engineers to try to produce artificial lighting which promotes plant growth. For instance energy inefficient “white light” sources may be modified to produce more light at wavelengths known to promote plant growth and health. This hybrid technology, in which the bulk of the light from these enhanced “plant grow lights” cannot be used efficiently by plants, has dominated the market for four decades.
In U.S. Pat. No. 6,921,182 it was found that the proportion of twelve red 660 nm LEDs plus six orange 612 nm LEDs and one blue 470 nm LED was optimal. The preferred circular lamp described accommodated two of these optimal sets of LEDs, resulting in a device with twenty-four red 660 nm LEDs, twelve orange 612 nm LEDs, and two blue 470 nm LEDs. Also, in U.S. Pat. No. 6,921,182 it was described to use mixed LED strings that contained both types of LEDs for enhanced wavelength mixing.
LEDs were used having two beam spreads of 15° and 30°, in equal proportions, for both the 660 nm LEDs and 612 nm LEDs. When LED light was directed perpendicularly to the upper surface of mature cotton plant leaves, it was found that a quantum light sensor placed below the leaf registered 10% light transmission for the 30° LEDs, and 80% light transmission for the 15° LED, and as much as 50% of the orange/red spectrum primarily used for photosynthesis was transmitted through the upper leaf canopy, making it available to support photosynthesis in leaves below.